Oil well cement and method of making the same

ABSTRACT

A cement composition for deep oil wells comprising sintered dicalcium silicate, uncombined calcium oxide, and silica. A method of making the cement in which a mixture of limestone and sand is sintered. For best efficiency the sintering is at a temperature between 2,500* and 2,560* F., and the raw mixture is proportioned to yield a sinter whose primary constituent has a molecular ratio of approximately 2 CaO to 1 SiO2. If the uncombined CaO in the sinter is below 2 percent, additional CaO is added. Silica is also added to the sinter.

United States Patent Maravilla 51 Mar. 21, 1972 154] OIL WELL CEMENT AND METHOD OF 3,145,774 8/l964 Patchen ..l06/98 MAKING THE SAME 3,336,143 8/1967 Van Dreser et al ..l06/63 [72] Inventor: Sam Maravilla, Lansing, lll. Primary Examiner james 5 Peer [73] Assignee: United States Steel Corporation Attorney-Martin J. Carroll [22] Filed: June 18, 1969 [57] ABSTRACT 21 A LN 834,538 I 1 pp 0 A cement composition for deep oll wells comprising sintered dicalcium silicate, uncombined calcium ozgide, ancLsjfig a. A Cl 106/ 100 method of making the cement in which a mixture of limestone [51] Int. Cl. ..C04b 7/02 and sand is i y For best ffi i the simering is at a [58] Field of Search ..106/63, 98, 100, 120 temperature between 2,500 a d 2,$60 F., and the raw mixture is proportioned to yield a sinter whose primary con- [56] References cued stituent has a molecular ratio of approximately 2 CaO to 1 UNITED STATES PATENTS SiO,. If the uncombined CaO in the sinter is below 2 percent,

additional CaO is added. Silica is also added to the sinter. 2,015,446 9/1935 Cape et al ..l06/63 2,2l0,326 8/l 940 Pitt et al. 106/63 11 Claims, No Drawings OIL WELL CEMENT AND METHOD OF MAKING THE SAME This invention relates to an oil well cementing composition composition of the limestone and sand may be as shown in Table l.

and to a method of making a sinter for use in the cementing TABLE] composition, and a method of making the cementing composi- 5 tion. The composition is particularly for use in a slurry for deep oil wells in which temperatures over 200 F. are present. Oil well cement slurries must have a retarded set since substantial time is required to pump them to their position of use. 060 Those oil well cements of which I have knowledge require the 8f: 7:: addition of retarding agents to conventional Portland ce- 0.0 ments. These cements have various disadvantages such as M10 0.65 0.40 non-uniformity and unpredictability of slurry behavior when exposed to oil well temperatures and pressures, and the cost of 35:52 providing additives.

It is therefore an object of my invention to provide a uniform oil well cement composition which has an adequate rate of hardening and an adequate rate of set at oil well tem- Pemmres and P The pellets are then dried and heated rapidly to a tempera- Alloihel' lg Provlde Such a Cement wh'ch does not ture between 2,500 and 2,560 F. preferably between 2,5 l0 requfre a v and 2,550 F. This may be done in a conventional rotary kiln hsnll anogherdob fgt 15:0 profvide sur]:h a corrilposrtgon whi with the maximum temperature being substantially below that w en com me wa er o a 5 no re uired in makin conventional Portland cement. When "t 2 g g zg if :f method of makmg usi ng the compositi n of Table l, a sinter is produced consistsm er use m v C F ing of 2.6 percent uncombined CaO and the remainder subg s' g gg g gz g provlde a method of makmg the stantially beta dicalcium silicate. The sinter is then ground to between 1,200 and 3,000 cm. and referabl between 3 22 gafg zgg zgzg mm apparem refs" 1,300 and 1,500 cm. lg. Wagnc r finenes s. To thi is added ri o l have found that si tered dicalcium silicate, when primarily 3322 13223 2: gi ggg ggg gz g gsZ3 2; 3;: L s j zg z zs 32 22122? 3 22:3222: zz g i sgisg oxides which are present in normal Portland cement may also While dicalcium silicate is one of several minerals produced in girz i ggg izf lz i xg zy i ri g 5:252:22; the manufacture of Portland cement clinker, it has never been p used an an oil well cement except with a substantial amount of 35 fg m we I b d b tricalcium silicate. However, I have found that a finely ground o my y l a so e F F. y composition consisting of 90 to 98 parts of dicalcium silicate a sinter conslstmg essenual of dlclclum ,slhcate primarily inbeta form, 10 to two parts of calcium oxide, with .havmg less man 2 Rercem upcombined 9 oxlde' To the total number of parts of the dicalcium silicate and calcium then added suffic'em calc'um Oxlde to false percent oxide being approximately lOO, and from 30 to 90 parts of sil- 40 age m at least 2 P ica can be used as an oil well cementing composition. All parts P 'denufies test samples of ground F referred to and percentages here and hereafter are by weight. Such a hereinafter. Samples 12 and 13 are conventional. Samples E, composition, when used in a slurry, will have a retarded set at and 9 Prepamf] from of hmcsmne f 24 of ordinary temperature and, after it is in place, hydration will f the analys's Show In Table of proceed at a sufficient rate to satisfy American Petroleum Inbone acld was f simples and 6 were F at a stitute (APl) requirements due to the presence of heat and Peralum of 2,735 2 F- While Sample E was sintered at a pressure in the oil well. The calcium oxide in the composition temperature of 2,530 :20 F other condmons being the may be supplied as a residual component in the sintered dicalsamecium silicate and/or as an addition to the sinter. The cement is preferably made as follows: A raw mix of limestone (essen- TABLE" tially CaCo and sand (essentially SiO in the required proportions to make dicalcium silicate are mixed together uniformly and pelletized in any standard manner. The raw mix proportions to obtain essentially dicalcium silicate (mostly f i z' Unmmbincd beta, but some gamma) should be such as to yield a sinter Tc" specific C30 whose primary constituent has a molecular ratio of approxi- Samples :25 M at cmlg in SinterZ mately 2CaO to l SiO although this ratio may vary somewhat. it is preferred to pre-grind lake sand to pass 200 mesh and the A "70 so limestone to pass 20 mesh. Then the raw mix consisting of-ZO B 83.4 2030 3.0 mesh limestone and 200 mesh sand in the correct molecular g 2;; :32: ratio plus 0.5 percent boric acid and 0.2 percent Methocel E H90 2 each by weight of the combined limestone and sand are inter- F 1150 0,6 ground so that 98.5 percent will pass 200 mesh. Boric acid is a G 17.3 1250 0.6 mineral stabilizer for BC S and inhibits its inversion to the 'l 3:"; 32: gamma form. Other well known stabilizers, such as borax and a "65 chromium oxide, may be used in place of the boric acid. The

TABLE III Other minor Loss on Total constit- S102 A120; FeiO; CBO MgO ignition alkalies uents Limestone 0. 0o 0. 2' 0.10 54. 4 o. as 44. 0 Nll 0. 0s and 87. 60 B. 30 l. 90 1.40 0. 40 0. 2. 2i 0. 43

Table IV shows the results of thickening time and compressive strength tests performed according to API recommended practice for oil well cements on cements of my invention produced in various ways. The silica flour added had a 1,400

it will be seen that my cement may be made either by making a sinter having the required uncombined calcium oxide and adding silica thereto or by making a sinter having an uncombined calcium oxide content ofless than that required and adding both silica and calcium oxide and/or calcium hydroxide thereto. The first method is preferred because of the lower The composition is mixed with water in the usual manner cm./g. Wagner specific surface and 60.6 percent passed 325 5 mesh. There was not sufficient sinter to perform the 24 hr. pressure test on samples A and B. The terms poises," units cost ofproduction. of consistency and Uc" are used interchangeably to denote consistency ofcement slurry. for use in deep oil wells.

TABLE IV API sched. 9, Compressive strength, p.s.i.,

16,000 it., 2' cu es thickening API Schedule o-aao F, Uncombined time, 3,000 p.s.l. curing pressure 0:20 in sinter, Water/solids 70 poises, Test sample percent ratio hr.:min. 8 hr. 24 hr.

.API Class F minimum requirements 1 3:10 500 000 .At100 U,,. k

TABLE V While it is preferred to pelletize the raw mix for various reasons, such as minimizing dustj'sses, obtaining uniform chemical composition and obtaining more uniform burning, l have found that my invention can also produce suitable cements when a powdered raw mix is sintered. in this case I have found that the sintering should be done at a temperature between 2,400 and 2,500 F. This method has the advantage that no special elletizing equipment is required.

Pan American thickening-time tester, API

Compressive stung}:

Added schedule 9-16,000 it. casing cementing 2 cubes. p.s.i., A

silica Mixing schedule 98, 320 F., flour, water, Thickening time, 3,000 p.s.i. curing percent wam-l Consistency, Ua hr.: min. pressure so s Test sample of sinter ratio Initial -30 min. 70 U 100 U, 8 hr. 24 hr,

0 0. 380 125 1, 265 10 0. 404 Test not made 225 2, 810 15 0. 396 325 5, 650 0. 435 10 16 1 :44 1:51 555 4, 690 0.435 8 8 3:22 3:24 1,200 5,750 0.435 2 4 3:30 3:42 1,060 5,525 0.435 6 7 3:21 3:25 1,620 5,125 0.435 5 5 3:28 3:31 1,695 3, 390 0. 427 5 5 3:14 3:22 1, 570 2, 915 0.421 6 6 3:10 3:17 1, 510 2,450 0. 421 5 6 3:26 3:39 1, 370 2, 585 0 0.380 10 36 0:36 0:38 3, 685 1, 980 40 0.395 7 19 0:42 0:44 2, 225 8. 940

API Class F requirements 30 I 3 10 I 500 I 1,000

1 Maximum.

I Minimum. 7 WWMW. e A r Table VI shows the results of adding calcium hydroxide and silica flour to ground sinter samples corresponding to test samples F and G, respectively.

in carrying out my experiments with a powdered feed I used sand identical to that of Table l and limestone as close to that of Table l as possible. The only difference was the negligible TABLE VI Thickening time tester API Schedule 9 Compressive strength 10,00015 2" Cubes, .54. Added Mixing APi Schedule 94, Total uncomsilica water, Thickening time, 32) F, 3,000 p.s.l.

bined CaO flour I water/ Consistency. U. hr.:min. curing pressure Added Ca(OH) adjusted percent solids percent of sinter 0e0 percent of sinter ratio Initial 15-30 min. 70 U. U. 8 hr. 24 hr.

API Class F reqnirements l 30 4 3:10 4 500 4 1,000

1 By weight of 8-028 sinter. 1 Includes CaO added as Ca(0H)1 plus residual or unoombined CaO in sinter. Maximum. 1 Minimum.

Q A l one of the Al o content being 0.20 percent instead of 0.62 percent.

Test Samples 16, 17, and 18 were made with Sample 16 being sintered at an average temperature of 2,455 F., Sample 17 at an average temperature of 2,420 F. and Sample 18 at an average temperature of 2,405 F. To each sample was added 40 percent by weight of silica flour by intergrinding the sinter and silica flour. A slurry was made with the water/solids ratio of each sample being 0.435. Table VI] shows the thickening time and strength data for these samples comparable to Tables IV and V.

2. The method of claim 1 in which the raw mixture is proportioned to yield a sinter whose primary constituent has a molecular ratio ofapproximately 2 (a to 1 SiO,.

3. The method of claim 1 which includes adding a mineral 5 stabilizer to the raw mixture, and in which the sintering is at a temperature between 2,400 and 2,600" F.

4. The method of claim 1 which includes adding at least one compound of the class consisting of CaO and Ca(OH,) to the sinter.

5. The method of claim I which includes pelletizing the raw mix, and in which the sintering is at a temperature between It will be seen that Test Sample 17 does not meet the minimum API compressive strength requirement at 8 hours, but this merely requires the addition of sufficient CaO to bring the total uncombined CaO content to 2 percent. The cement ofTest Sample 18 is preferred.

l have found that the sinter produced using a powdered feed has more minor constituents than a sinter produced using a pellet feed. For example, the sinter of Test Sample 18 has a CaO to SiO ratio of only 1.61 percent as compared to a ratio of l.97 for Test Sample 6.

The cements produced according to any of the above methods must contain from 90 to 98 parts by weight of sintered dicalcium silicate, between 10 and two parts by weight of uncombined calcium oxide, the total number of parts of dicalcium silicate and calcium oxide being I00, from 30 to 90 parts by weight of silica, and the remainder minor constituents normally present in Portland cements.

While several embodiments of my invention have been described, it will be apparent that other embodiments and compositions may be made.

lclaim:

l. The method of making an oil well cement containing from two to 10 parts by weight of uncombined CaO, 98 to 90 parts by weight of dicalcium silicate, from 30 to 90 parts ofsilica and minor constituents, which method comprises sintering a raw mixture of ground limestone and sand in the correct molecular ratio to obtain dicalcium silicate, then grinding said sinter, and adding silica flour to said sinter.

2.,500 and 2,560 F.

6. The method of making a sintered product containing from 2 to 10 percent by weight uncombined C30 and the remainder essentially dicalcium silicate and minor constituents, which method comprises sintering a dry unbonded mixture in the form of small particles consisting essentially of limestone and sand by rapidly heating the mixture to a temperature between 2,400 and 2,600 F. said raw mixture being proportioned to yield a sinter whose primary constituent has a molecular ratio of approximately 2 CaO to 1 SiO,.

7. The method of claim 6 which includes adding a mineral stabilizer to the raw mixture.

8. The method of claim 7 which includes pelletizing the raw mix, and in which the sintering is at a temperature between 2,500 and 2,5600 F.

9. A finely ground oil well cementing composition consisting of 90 to 98 parts by weight of sintered dicalcium silicate, between 10 and two parts by weight of uncombined calcium oxide, the total number of parts of dicalcium silicate and calcium oxide being 100, from 30 to 90 parts by weight of silica and the remainder minor constituents normally present in Fortland cements.

10. An oil well cementing composition according to claim 9 in which the components have a Wagner fineness between 1,200 and 3,000 cm /g. 11. An oil well slurry consisting of the composition of claim 10 and water. 

2. The method of claim 1 in which the raw mixture is proportioned to yield a sinter whose primary constituent has a molecular ratio of approximately 2 CaO to 1 SiO2.
 3. The method of claim 1 which includes adding a mineral stabilizer to the raw mixture, and in which the sintering is at a temperature between 2,400* and 2,600* F.
 4. The method of claim 1 which includes adding at least one compound of the class consisting of CaO and Ca(OH2) to the sinter.
 5. The method of claim 1 which includes pelletizing the raw mix, and in which the sintering is at a temperature between 2,500* and 2,560* F.
 6. The method of making a sintered product containing from 2 to 10 percent by weight uncombined CaO and the remainder essentially dicalcium silicate and minor constituents, which method comprises sintering a dry unbonded mixture in the form of small particles consisting essentially of limestone and sand by rapidly heating the mixture to a temperature between 2,400* and 2,600* F. said raw mixture being proportioned to yield a sinter whose primary constituent has a molecular ratio of approximately 2 CaO to 1 SiO2.
 7. The method of claim 6 which includes adding a mineral stabilizer to the raw mixture.
 8. The method of claim 7 which includes pelletizing the raw mix, and in which the sintering is at a temperature between 2,500* and 2,5600* F.
 9. A finely ground oil well cementing composition consisting of 90 to 98 parts by weight of sintered dicalcium silicate, between 10 and two parts by weight of uncombined calcium oxide, the total number of parts of dicalcium silicate and calcium oxide being 100, from 30 to 90 parts by weight of silica and the remainder minor constituents normally present in Portland cements.
 10. An oil well cementing composition according to claim 9 in which the components have a Wagner fineness between 1,200 and 3, 000 cm2/g.
 11. An oil well slurry consisting of the composition of claim 10 and water. 